[LE.UM.2.3.2.r1.4] [SECURITY] perf: core: Avoid race condition when releasing perf-events#2000
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jerpelea merged 1 commit intosonyxperiadev:aosp/LE.UM.2.3.2.r1.4from Jun 13, 2019
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The function, perf_event_release_kernel(), that's used to free the perf events is dependent on the CPU associated to this event be online. The function checks at the beginning: if the CPU is offline, put it in a zombie list and return immediately. Else, proceed and make a cross-cpu call (from perf_remove_from_context()) to complete the functionality. However, there's a potential chance of a race if the CPU went offline between the initial check and the cross-cpu call. The cross-cpu call deletes the event from the context's list, but if the CPU is offline, this deletion doesn't happen. Later the event is freed irrespective of this failure and the event still exists in the list. Now, when the list is traversed, it would try to access the memory which is freed, resulting in a memory abort. As a result, before calling perf_event_release_kernel(), capture the perf's pmus_mutex lock to prevent the CPU from going offline during the operation. Change-Id: I20241639ea9a8dc87e5a88cf81e940b3d6cb773c Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org> Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>
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This is the only part of the 2019-06-05 kernel security patches that we need to apply.
https://source.android.com/security/bulletin/2019-06-01.html#kernel-components